package hot100;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class b3_三数之和 {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        int len = nums.length;
        if(nums == null || len < 3){
            return res;
        }
        Arrays.sort(nums);
        for(int i = 0; i < len; i++){
            if(nums[i] > 0){
                break;
            }
            if(i > 0 && nums[i] == nums[i-1]){
                continue;
            }
            int left = i + 1;
            int right = len - 1;
            while(left < right){
                int sum = nums[i] + nums[left] + nums[right];
                if(sum == 0){
                    res.add(Arrays.asList(nums[i], nums[left], nums[right]));
                    while(left < right && nums[left] == nums[left + 1]){
                        left++;
                    }
                    while(left < right && nums[right] == nums[right - 1]){
                        right--;
                    }
                    left++;
                    right--;
                }
                else if(sum < 0){
                    left++;
                } else if (sum > 0) {
                    right--;
                }
            }
        }
        return res;

    }
}
